An electrophotographic printer having a developing cartridge detachably mounted therein is well known in the art. Conventionally, this type of developing cartridge has been provided with a detected rotary body that an external sensor can detect to learn information about the developing cartridge.
One example of this developing cartridge includes a housing that accommodates toner, and the detected rotary body and an agitator gear both provided on a side wall constituting the housing. The detected rotary body is provided with a disc-shaped sector gear part having gear teeth along a portion of its circumferential surface, a detected part provided on a left endface of the sector gear part, and a pressed part provided on a right endface of the sector gear part. The agitator gear is provided with a large-diameter gear part provided to the right of the sector gear part constituting the detected rotary body, a small-diameter gear part provided on the left side of the large-diameter gear part, and a pressing part provided on a left endface of the large-diameter gear part (see Japanese Patent Application Publication No. 2011-215374, for example).
In this conventional developing cartridge, a drive force is transmitted to the agitator gear for rotating the agitator gear. When the agitator gear rotates, the pressing part on the agitator gear presses against the pressed part of the detected rotary body. The pressure from the pressing part rotates the detected rotary body until the gear teeth provided on the portion of the sector gear part intermesh with the small-diameter gear part of the agitator gear. Consequently, the drive force transmitted to the agitator gear is further transmitted to the detected rotary body to rotate the same. During this rotation, the detected rotary body moves from an initial first position away from the side wall of the housing to a second position, which is the position farthest separated from the side wall, and subsequently begins to move again closer to the side wall until arriving at a third position.